Environment variables are not cleaned up

[aurelienshz]

Hey there! 👋

We're using this image (phusion/passenger-ruby25:1.0.5) to run a Rails app, and we are not seeing the behavior documented at https://github.com/phusion/passenger-docker#setting-environment-variables-in-nginx. Environment variables that are set up through Docker Compose .env mechanism are visible to the Rails app.

My question is:

• if this expected? If so, should the documentation be updated? (happy to submit a PR)
• otherwise, should this be fixed?

My biggest concern is that this is fixed inadvertently in a further version, and apps suddenly start breaking for obscure reasons when updating the Phusion Passenger image version.

Reproduction steps

We are using docker-compose. Here are relevant extracts and reproduction steps:

# docker-compose.yml:
services:
  app:
    build: .
    environment:
      TEST_ENV_VAR: ${TEST_ENV_VAR}

# .env
TEST_ENV_VAR=test1234

# Dockerfile:
FROM phusion/passenger-ruby25:1.0.5
# Allow nginx to pass environment variables to the app at runtime:
COPY ./docker/env.conf /etc/nginx/main.d/env.conf
# [...] Copy the app's files, install dependencies, etc.

env.conf does not contain any line like env TEST_ENV_VAR;, yet the following is possible:

$ sudo docker-compose build
$ sudo docker-compose up -d
$ sudo docker-compose exec app bash
# The environment variable is in the container's environment:
root@c4503f22222e:/home/app# printenv | grep TEST_ENV_VAR
TEST_ENV_VAR=test1234
# Our nginx config doesn't contain anything to pass the env var to the child processes:
root@c4503f22222e:/home/app# cat /etc/nginx/main.d/db-env.conf | grep TEST_ENV_VAR
# Yet Rails has loaded the environment variable:
root@c4503f22222e:/home/app# cd webapp/
root@c4503f22222e:/home/app/webapp# bin/rails c
Running via Spring preloader in process 3004
Loading production environment (Rails 5.2.0)
2.5.1 :001 > ENV['TEST_ENV_VAR']
 => "test1234" 

[CamJN]

I believe rails c starts a copy of your app running as a child of your shell, rather than attach to the app running under nginx. So I think this is a red-herring.

[aurelienshz]

Ah... Maybe my repro steps are not perfectly describing the issue. But I can confirm that the web app we're running is getting those environment variables as well. They're critical to the app, and they're marked as mandatory using a Figaro initializer (which means the app wouldn't even start if they weren't defined).

[CamJN]

Well, I'd be open to a PR to document additional ways to set env vars.

[aurelienshz]

I'm not quite sure I understand how this is an additional way to set an env var.

The variable is set up in the container's environment (using docker-compose, but under the hood, it's the same thing as using -e on the docker command), and it's visible to the Rails app without setting up any env instructions in the Nginx config. I may be misunderstanding the documentation at https://github.com/phusion/passenger-docker#setting-environment-variables-in-nginx, but it feels to me like the documentation describes this as impossible, yet it is working perfectly fine.

I'm totally fine with it, as long as this is not a bug which will be fixed in a future version and may break apps very unexpectedly.